1. Field of the Invention
The present invention relates to a metal gate electrode, for example. In particular, it relates to a method of manufacturing a semiconductor device that has an n-type metal oxide semiconductor field-effect transistor (MOSFET) and a p-type MOSFET having metal gate electrodes of different compositions.
2. Background Art
According to prior art, a metal gate electrode is used to suppress the gate depletion layer of a MOS transistor. A fully silicided (FUSI) gate is preferably used because it is suitable for currently available manufacturing methods for a semiconductor device.
However, the FUSI gate is difficult to control the work function. The work function of the FUSI gate (threshold voltage of MOSFET with the FUSI gate) can be changed by implanting As, P or B in the gate insulating film made of SiO2. However, this approach has a problem that the work function (threshold voltage) cannot be controlled to a desired value.
In addition, a high dielectric insulating film, rather than the SiO2 film, can be used as the gate insulating film in order to suppress the leak current at the gate.
The high dielectric insulating film may be a hafnium silicate nitride (HfSiON) film. However, compared with the case of changing the composition of the gate electrode (NixSiy, for example), the variable range of the threshold voltage is narrow.
Thus, according to a conventional method of manufacturing a semiconductor device, a FUSI gate having a threshold closer to a desired value is formed by changing the composition of the FUSI gate or combining other materials to form the FUSI gate (Japanese Patent Laid-Open Publication No. 2005-167251).
In the conventional method, Ni is deposited on the gate made of polysilicon to cause silicidation of the polysilicon gate. Then, using a TiN protective film, the Ni is selectively removed with a mixture of hydrochloric acid and hydrogen peroxide depending on the structures of the p-type MOS and the n-type MOS. Then, a thermal processing is performed to cause selective silicidation of polysilicon of the gate.
However, the conventional method has a disadvantage that the Ni on the polysilicon cannot be adequately removed with the mixture of hydrochloric acid and hydrogen peroxide, and therefore, a desired threshold cannot be provided.